const fs = require('fs');
const os = require('os');
const path = require('path');

var inDir;
if ('darwin' === os.platform()) {
    inDir = os.homedir() + '/Library/Containers/com.tencent.QQMusicMac/Data/Library/Application Support/QQMusicMac/iQmc';
} else {
    inDir = os.homedir() + '/AppData/QQ音乐';
}
const outDir = os.homedir() + '/Music/QQ音乐';

(async () => {
    const files = fs.readdirSync(inDir);
    if (!fs.existsSync(outDir)) {
        fs.mkdirSync(outDir);
    }
    for (let i = 0; i < files.length; ++i) {
        const src = path.join(inDir, files[i]);
        const ext = path.extname(src);
        let ext2 = '.mp3';
        if (ext === '.qmcflac') {
            ext2 = '.flac';
        } else if (ext === '.qmc0' || ext === '.qmc3') {
            ext2 = '.mp3';
        } else {
            console.log('Warning: unknown extname (support: qmcflac, qmc0, qmc3).');
            continue;
        }
        const dst = path.join(outDir, path.basename(src, ext) + ext2);
        if (!fs.existsSync(dst)) {
            await encrypt(src, dst);
        }
    }
})().catch(err => console.log(err));

function encrypt(src, dst) {
    return new Promise((resolve, reject) => {
        console.log(fs.basename(src), '=>', dst);
        const is = fs.createReadStream(src);
        const os = fs.createWriteStream(dst);
        let offset = 0;
        is.on('data', function(chunk) {
            const length = chunk.length;
            const buf = Buffer.alloc(length)
            for (let i = 0; i < length; i++) {
                buf[i] = chunk[i] ^= mapL(offset + i);
            }
            os.write(buf);
            offset += length;
        });
        is.on('error', function(err) {
            reject(err);
        });
        is.on('end', function() {
            resolve();
        });
    })
}

function mapL(v) {
    const key = [
        0x77, 0x48, 0x32, 0x73, 0xDE, 0xF2, 0xC0, 0xC8, 0x95, 0xEC, 0x30, 0xB2,
        0x51, 0xC3, 0xE1, 0xA0, 0x9E, 0xE6, 0x9D, 0xCF, 0xFA, 0x7F, 0x14, 0xD1,
        0xCE, 0xB8, 0xDC, 0xC3, 0x4A, 0x67, 0x93, 0xD6, 0x28, 0xC2, 0x91, 0x70,
        0xCA, 0x8D, 0xA2, 0xA4, 0xF0, 0x08, 0x61, 0x90, 0x7E, 0x6F, 0xA2, 0xE0,
        0xEB, 0xAE, 0x3E, 0xB6, 0x67, 0xC7, 0x92, 0xF4, 0x91, 0xB5, 0xF6, 0x6C,
        0x5E, 0x84, 0x40, 0xF7, 0xF3, 0x1B, 0x02, 0x7F, 0xD5, 0xAB, 0x41, 0x89,
        0x28, 0xF4, 0x25, 0xCC, 0x52, 0x11, 0xAD, 0x43, 0x68, 0xA6, 0x41, 0x8B,
        0x84, 0xB5, 0xFF, 0x2C, 0x92, 0x4A, 0x26, 0xD8, 0x47, 0x6A, 0x7C, 0x95,
        0x61, 0xCC, 0xE6, 0xCB, 0xBB, 0x3F, 0x47, 0x58, 0x89, 0x75, 0xC3, 0x75,
        0xA1, 0xD9, 0xAF, 0xCC, 0x08, 0x73, 0x17, 0xDC, 0xAA, 0x9A, 0xA2, 0x16,
        0x41, 0xD8, 0xA2, 0x06, 0xC6, 0x8B, 0xFC, 0x66, 0x34, 0x9F, 0xCF, 0x18,
        0x23, 0xA0, 0x0A, 0x74, 0xE7, 0x2B, 0x27, 0x70, 0x92, 0xE9, 0xAF, 0x37,
        0xE6, 0x8C, 0xA7, 0xBC, 0x62, 0x65, 0x9C, 0xC2, 0x08, 0xC9, 0x88, 0xB3,
        0xF3, 0x43, 0xAC, 0x74, 0x2C, 0x0F, 0xD4, 0xAF, 0xA1, 0xC3, 0x01, 0x64,
        0x95, 0x4E, 0x48, 0x9F, 0xF4, 0x35, 0x78, 0x95, 0x7A, 0x39, 0xD6, 0x6A,
        0xA0, 0x6D, 0x40, 0xE8, 0x4F, 0xA8, 0xEF, 0x11, 0x1D, 0xF3, 0x1B, 0x3F,
        0x3F, 0x07, 0xDD, 0x6F, 0x5B, 0x19, 0x30, 0x19, 0xFB, 0xEF, 0x0E, 0x37,
        0xF0, 0x0E, 0xCD, 0x16, 0x49, 0xFE, 0x53, 0x47, 0x13, 0x1A, 0xBD, 0xA4,
        0xF1, 0x40, 0x19, 0x60, 0x0E, 0xED, 0x68, 0x09, 0x06, 0x5F, 0x4D, 0xCF,
        0x3D, 0x1A, 0xFE, 0x20, 0x77, 0xE4, 0xD9, 0xDA, 0xF9, 0xA4, 0x2B, 0x76,
        0x1C, 0x71, 0xDB, 0x00, 0xBC, 0xFD, 0xC, 0x6C, 0xA5, 0x47, 0xF7, 0xF6,
        0x00, 0x79, 0x4A, 0x11
    ];
    if (v >= 0) {
        if (v > 0x7FFF) v %= 0x7FFF;
    } else {
        v = 0;
    }
    return key[(v * v + 80923) % 256];
}